At first MgNb2O6 (orthorhombic)was synthesized as well as made hybrid compound with Ag deposition (Ag-MgNb2O6).After analyzing Ag was found as a cubic particle on the surface as well as exist in interlayer of MgNb2O6 but not intralayer.
For doping case, always exist A/b site then it`s easy to make the structure. But in the case of deposition Ag did not enter into the intralayer of MgNb2O6 just staying in the interlayer (surface on the MgNb2O6) of the MgNb2O6.
As Padmaja says, it can be done!
To give an explanation; if you have a periodic crystal you can use CASTEP to simulate a band structure and a DOS.
For a surface (which it sounds like you are modelling), this appears to be an aperiodic boundary, and therefore to be incompatible with a periodic boundary simulation; this is not, however, the case!
You can model a surface by adding in a "vacuum gap", which essentially means increasing the size of your lattice vectors in the out-of-plane direction, but not filling it with any atoms (so there is just vacuum there!). Converging this distance is important to get accurate results, and I would typically consider that 12 angstroms of *vacuum* to be a good rule of thumb to start the convergence testing (although typically the converged value will be larger than this).
You may also wish to investigate hydrogen passivation for the bottom surface of the slab, as this can help to minimise the vacuum required.
A final subtlety for slabs like this is that the large out-of-plane lattice vector means that the size of the Brillouin zone in that direction decreases, which means that you only need to consider a 2D band structure (compare the band structures of graphite and graphene in the literature if you want to see this in action!)
Hope that helps,
Robert
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